We used Seattle's new light rail from/to Airport and Downtown. It's only 2.50 each way. Beats paying $50 for a one-way cab ride. The train ran every 7-10 minutes. I never waited more than 1 minute to get on a train. It was very clean and I felt very safe. All very nice and friendly looking people using the train.
The only drawback is you have to walk a little ways at the airport to get to the light rail station. But it would be the same or longer to get a cab or rent a car. So the light rail wins there.
I will use it again and I will recommend it to anyone who asks.